1. Field of the Invention
The present invention relates to a process cartridge, a method for assembling a process cartridge and an image forming apparatus having the cartridge. The image forming apparatus may be, for example, a laser beam printer, an electrophotographic copying machine, a facsimile machine, a word processor or the like.
2. Related Background Art
In the past, a so-called process cartridge wherein a photosensitive drum, a charger, a developing device, a cleaning device and the like are integrally contained in a cartridge housing, which can be removably mounted to an image forming apparatus, has been put into practical use (for example, as disclosed in U.S. Pat. Nos. 3,985,436, 4,500,195, 4,540,268 and 4,627,701).
Generally, a photosensitive drum is electrically earthed at keep the charging charge on a surface of the drum to a predetermined constant value. Further, a charger means is supplied with a voltage to uniformly charge the photosensitive drum and a developing device is also supplied with a voltage to form a toner image on the photosensitive drum. Accordingly, when an image forming station is constituted by a process cartridge, the cartridge must have electric contacts for electrical connection to an image forming apparatus.
However, for example, when an electric contact for electrically earthing the photosensitive drum is positioned near an electric contact for applying an AC voltage, and particularly, an electric contact for applying a charging voltage, the following disadvantages are apt to occur. That is to say, when the process cartridge is mounted to the image forming apparatus, the electric contact of the cartridge for applying the AC voltage is electrically connected to the electric contact of the apparatus for applying the AC voltage.
On the other hand, the electric contact of the cartridge for applying the AC voltage is connected to a power source via wiring. Accordingly, if the electric contact for electrically earthing the photo-sensitive drum is positioned near the electric contact for applying the charging voltage, the earthing contact will be disposed near the AC wiring of the apparatus, thus generating a stray capacity between the earthing contact and the AC wiring. The stray capacity causes the escape of current that was to be applied to the charger, from the AC wiring to the earthing contact, thereby worsening the ability of the charger.
Further, in an apparatus wherein AC voltages are applied to both a developing device and a charger, if the AC voltage applying contacts are arranged near each other, interference will occur between the contacts. That is to say, generally, since the charging voltage has a frequency lower than that of the developing voltage, the value of the charging voltage is changed by such interference, thus causing a charging discrepancy.